Far and away, the two best music soundtracks are from two PC strategy games. Fantasy General and Heroes of Might and Magic 2. Nothing else is even close. If you haven't heard these two, I highly recommend picking them up (you can probably Ebay them for about $2 now) and giving them a listen.

The Castlevania series has a lot of fantastic music, especially Symphony of the Night.And while I've come to mostly dislike the Megaman series, I do enjoy pretty much all its music.I actually like most of the tyrant themes for Resident Evil games, especially "The 2nd Malformation of G" from RE2.

Cobra mentioned that he likes Donkey Kong Country's water music tracks; I'd have to agree with you there. My particular favorite is DKC 3's water theme.

I guess I don't have a specific track I could proclaim is greatest. My taste shifts around too much.And I have way too many favorites, usually a handful from each game's sountrack. To list them all would be inane.